Cartilage l General Histology & Biology MCQs for dental students

Cartilage (light microscope , electron microscope, structure and function) l General Histology & Biology MCQs for dental students

 

Cartilage

• Cartilage is a firm flexible CT formed of cartilage cells in a rubbery extracellular matrix (formed of CT fibers "collagen type II" and ground substance).
• It is non-vascular and covered by perichondrium.

Function of cartilage:

1. Support of the body (by skeleton).
2. Protection of essential organs (as CNS, heart, lung ...).
3. Bone growth in length by intra-cartilaginous ossification.
4. Opening of airway (nose, larynx, trachea and bronchi).
5. Formation of smooth surface for joint movement.

Structure of cartilage:

Cartilage cells:

Chondroblasts (immature cartilage cells):

Origin:

• arise from UDMCs (un-differentiated mesenchymal cells).

Site:

• present singly at the periphery of cartilage (under perichondrium).

Light microscope :

• oval deep basophilic cells with oval nuclei.

Electron microscope :

• features of protein-forming cells (as they form extracellular matrix).

Function:

• transformed to chondrocytes ® peripheral appositional growth.

Chondrocytes (mature cartilage cells):

Origin:

• arise from chondroblasts.

Site:

• present at the center of cartilage in groups "cell nests" formed of 2, 4 or 8 cells surrounded by space "lacuna" and capsule (of condensed matrix).

Light microscope :

• rounded pale basophilic cells with rounded nuclei.

Electron microscope :

• features of protein-forming cells (as they form extracellular matrix) with glycogen and lipid droplets.

Function :

• divide ® central interstitial growth.

Note book :

• chondroblasts and chondrocytes form extracellular matrix so they have EM features of protein forming cells ( euchromatic pale nucleus with prominent nucleoli - many mitochondria, many rough endoplasmic reticulum , well developed Golgi apparatus and many secretory vesicles).

Fibers :

• collagenous fibers "type II" and elastic fibers.

Ground substance:

• tissue fluid containing glycos-amino-glycans ( GAGs ) causing its basophilia, proteoglycans (as chondroitin sulphate, hyaluronic acid …) and glycoprotein.

Perichondrium:

vascular CT membrane formed of 2 layers:

1. Outer fibrous layer (formed of collagenous bundles "type I" and fibroblasts): for muscle attachment.
2. Inner chondrogenic layer (formed of chondroblasts): for nourishment (by diffusion) and peripheral appositional growth (increase in width by formation of new chondroblasts and their transformation to chondrocytes ).

Types of cartilage:

1. Hyaline cartilage:

• It is translucent and common.
• Present in fetal skeleton - costal cartilage - respiratory passages (nose, larynx, trachea and bronchi) - articular surfaces of joints (but without perichondrium).
• Formed of cartilage cells, basophilic matrix (containing collagen fibers) and perichondrium.

2. Elastic cartilage:

• It is yellow and stretchable.
• Present in ear pinna, external auditory canal, epiglottis and eustachian tube.
• Formed of cartilage cells, basophilic matrix (containing branching elastic fibers) and perichondrium.

3. Fibro-cartage:

• It is white and flexible.
• Present in inter-vertebral discs and knee joints - symphysis pubis - mandibular joints - tendon of muscles.
• Formed of rows of cartilage cells separated by few acidophilic matrix ( containing thick collagenous fibers "type I" ).

Note book :

• White fibro-cartage has no perichondrium (but only vascular dense fibrous tissue for nourishment).

 

Growth of cartilage:

• Growth of cartilage occurs by two ways:

1. Peripheral (appositional) growth:

• Formation of new chondroblasts and their transformation to chondrocytes ® increase of cartilage in width.

2. Central (interstitial) growth:

• Mitotic division of chondrocytes and secretion of more matrix ® increase of cartilage in length.